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7/24/2019 Eddy Current Brakes Seminar Report
1/23
Seminar Report 2004 Eddy Current Brake
ABSTRACT
This is an electric braking system which works on the principle that eddy
current produced in it opposes the driing tor!ue" This opposing tor!ue is used to
brake the automobiles" #ainly this system is purely based on $araday%s laws o&
electromagnetic induction and 'en(%s law"
$or operating this a control switch is proided on the steering column in a
position &or easy manual" The skidding and comple)ity o& mechanical braking system
can be minimi(ed by this system" Also the wear and tear o& the ehicles can be
reduced"
Since researches are going on to eliminate some o& the disadantages o& this
system* we can accept it to be the norm one in a &ew years o& time"
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Seminar Report 2004 Eddy Current Brake
C/TETS
." 1TR/+CT1/
2" 3R1C13'E /$ /3ERAT1/
" C/STRCT1/
4" 5/R-16
7" E++8 CRRET BRA-E 1 TRA1S
9" BRA-16 3/5ER CA'C'AT1/S
:" E++8 CRRET BRA-E RE;1RE#ETS
ATA6ES
.0" +1SA+>ATA6ES
.." A33'1CAT1/S
.2" C/C'S1/
." RE$ERECES
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Seminar Report 2004 Eddy Current Brake
1TR/+CT1/
#any o& the ordinary brakes* which are being used now days stop the ehicle
by means o& mechanical blocking" This causes skidding and wear and tear o& the
ehicle" And i& the speed o& the ehicle is ery high* the brake cannot proide that
much high braking &orce and it will cause problems" These drawbacks o& ordinary
brakes can be oercome by a simple and e&&ectie mechanism o& braking system ?The
eddy current brake%" 1t is an abrasion@&ree method &or braking o& ehicles including
trains" 1t makes use o& the opposing tendency o& eddy current
Eddy current is the swirling current produced in a conductor* which is
subected to a change in magnetic &ield" Because o& the tendency o& eddy currents to
oppose* eddy currents cause energy to be lost" #ore accurately* eddy currents
trans&orm more use&ul &orms o& energy such as kinetic energy into heat* which is
much less use&ul" 1n many applications* the loss o& use&ul energy is not particularly
desirable" But there are some practical applications" Such an application is the eddy
current brake"
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Seminar Report 2004 Eddy Current Brake
3R1C13'E /$ /3ERAT1/S
Eddy current brake works according to $araday%s law o& electromagnetic
induction" According to this law* wheneer a conductor cuts magnetic lines o& &orces*
an em& is induced in the conductor* the magnitude o& which is proportional to the
strength o& magnetic &ield and the speed o& the conductor" 1& the conductor is a disc*
there will be circulatory currents i"e" eddy currents in the disc" According to 'en(%s
law* the direction o& the current is in such a way as to oppose the cause* i"e" moement
o& the disc"
Essentially the eddy current brake consists o& two parts* a stationary magnetic
&ield system and a solid rotating part* which include a metal disc" +uring braking* the
metal disc is e)posed to a magnetic &ield &rom an electromagnet* generating eddy
currents in the disc" The magnetic interaction between the applied &ield and the eddy
currents slow down the rotating disc" Thus the wheels o& the ehicle also slow down
since the wheels are directly coupled to the disc o& the eddy current brake* thus
producing smooth stopping motion"
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Seminar Report 2004 Eddy Current Brake
E++8 CRRET 1+CE+ 1 A C/+CT/R
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C/STRCT1/
Essentially an eddy current brake consists o& two members* a
stationary magnetic &ield system and a solid rotary member* generally o& mild steel*
which is sometimes re&erred to as the secondary because the eddy currents are
induced in it" Two members are separated by a short air gap* they%re being no contact
between the two &or the purpose o& tor!ue transmission" Conse!uently there is no
wear as in &riction brake"
Stator consists o& pole core* pole shoe* and &ield winding" The &ield
winding is wounded on the pole core" 3ole core and pole shoes are made o& east steel
laminations and &i)ed to the state o& &rames by means o& screw or bolts" Copper and
aluminium is used &or winding material the arrangement is shown in &ig" ." This
system consists o& two parts"
1. Stator
2. Rotor
Stator:-
1t is supported &rame members o& the ehicle chassis" 1t has introduced
magnetic poles energi(ed by windings" Current is supplied to the winding &rom the
battery"
Rotor:-
1t is a rotating disc* which is &itted on the line o& cranksha&t with small air gap to
stator" 5hen disc rotates a &lu) change occur in the section o& the disc passing the
poles o& stator" +ue to the &lu) change there is a circulatory or eddy current in the
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Seminar Report 2004 Eddy Current Brake
disc around the magnetic lines o& &orce" The e&&ect o& this eddy current induces ?%
and ?S% poles at the sur&ace o& the disc" Then there will be a ?drag% or braking e&&ect
in between eddy current induced poles and magnetic poles in the stator" By
changing current &rom the battery we can change the braking &orce" 1n this breaking
system kinetic energy o& the ehicle is conerted to heat and this heat is dissipated
through the rotating disc"
Total resistance o& &ield winding
R 'A
where* ' total length o& &ield winding in meter"
Resistiity o& the wire in ohm meter
A the area o& cross section o& &ield winding in m2
Total noD o& terms total length mean length o& one term
The rotor is a rotating disc on sha&t* which is placed ery near to the stator
with small air gap . mm to 2 mmF" Rotating disc may be one or both side o& stator"
The two units hae common ring member* poles cores on which winding are
proided being &i)ed to ring number" 1& a malleable casting is employed* then the pole
core could be cast integrally with the right" A&ter &itting the windings on the cores*
poles shoes are &itted to proide pole &aces o& appropriate shape and area" The rotor
disc should be proided with properly designed &ins &or &aster heat remoal" The
magnetic circuits o& the two units are substantially the same* non@undue and thrust
would be imposed on the motor bearings" Slight a)ial displacement o& rotor could
howeer* cause !uite appreciable discrepancy* the air gap o& two units" The e&&ect
would be to increase the magnetic pull in one air gap and diminish it on other which
could gie to rise to e)cessie and thrust on rotor bearing to oercome the inherent
de&ect* the air gaps o& both units could be put in series by making the central number
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Seminar Report 2004 Eddy Current Brake
non magnetic and proiding a continues pole core &or each pair a)ially opposite poles"
This modi&ication could possibly reduce the length o& the combined pole course or
permits a larger winding length"
The ma)imum diameter o& the eddy current brake is decided by
." The spacing o& ehicle chassis &rame"
2" >ehicle &loor clearance
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5/R-16
5hen the ehicle is moing* the rotor disc o& eddy current brake which is
coupled to the wheels o& the ehicle rotates* in close pro)imity to stationary magnetic
poles" 5hen we want to brake the ehicle* a control switch is put on which is placed
on the steering column in a position &or easy operation"
5hen the control switch is operated* current &lows &rom a battery to the &ield
winding* thus energi(ing the magnet" Then the rotating disc will cut the magnetic
&ield" 5hen the disc cuts the magnetic &ield* &lu) changes occur in the disc which is
proportional to the strength o& the magnetic &ield" The current will &low back to the
(ero &ield areas o& the metal plate and thus create a closed current loop like a whirl or
eddy" A &low o& current always means there is a magnetic &ield as well" +ue to 'en(%s
law* the magnetic &ield produced by the eddy currents works against the moement
direction" Thus instead o& mechanical &riction* a magnetic &riction is created" 1n
conse!uence* the disc will e)perience a GdragH or the braking e&&ect* and thus the disc
stops rotation" The wheels o& the ehicle* which is directly coupled to the disc* also
stop rotation" $aster the wheels are spinning* stronger the e&&ect* meaning that as the
ehicle slows* the braking &orce is reduced producing a smooth stopping action"
The control switch can be set at di&&erent positions &or controlling the
e)citation current to seeral set alues in order to regulate the magnetic &lu) and
conse!uently the magnitude o& braking &orce" i"e" i& the speed o& the ehicle is lpw* a
low braking &orce is re!uired to stop the ehicle" So the control switch is set at the
lowest position so that a low current will be supplied to the &ield winding" Then the
magnetic &ield produced will be o& low strength* so that a re!uired low braking &orce
is produced"
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5hen the control switch is operated during the standby position o& the
ehicle* the magnet will be energi(ed and magnetic &ield is created" But since the
wheels are not moing* magnetic lines o& &orce are not cut by it* and the brake will not
work" Ioweer* a warning lamp is proided on the instrument panel to indicate
whether the brake is energi(ed" This proides a sa&e guard &or the drier against
leaing the unit energi(ed"
5hen control switch is put in any one o& the operating positions* the
corresponding conductor in the contractor bo) is energi(ed and current &lows &rom the
battery to the &ield winding to the contractor bo)" This current magneti(es the poles
in stator* which placed ery near to the rotor" 5hen rotor rotates it will cut magnetic
lines and eddy current will set up in the rotor" The magnetic &ield o& this eddy current
produces a breaking &orce or tor!ue in the opposite direction o& rotation disc" This
kinetic energy o& rotor is conerted as heat energy and dissipated &rom rotating disc
to surrounding atmosphere" Current in the &ield can change by changing the position
o& the controls switch" Thus we can change the strength o& the braking &orce"
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E++8 CRRET BRA-E 1 TRA1S
1n the case o& trains* the part in which the eddy current is induced is rail" The
brake shoe is enclosed in a coil* &orming an electromagnet" 5hen the magnet is
energi(ed* eddy currents are induced in the rail by means o& electromagnetic
induction* thereby producing braking action"
E++8 CRRET BRA-E 1 TRA1S
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+1STR1BT1/ /$ #A6ET1C $'J +ES1T8
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T83ES /$ E++8 CRRET BRA-ES
There are two types o& eddy current brakes according to the method o&
e)citation"
."Electrically e)cited eddy current brake
2"3ermanent magnet eddy current brake
."E'ECTR1CA''8 EJC1TE+ E++8 CRRET BRA-E
Electrically e)cited eddy current brakes are abruption@&ree method &or
braking" 1n high@speed trains they o&&er a good alternatie to the mechanical rail
brakes which are being used now a days" +uring braking* the brake comes in contact
with the rail* and the magnetic poles o& brakes are energi(ed by a winding supplied"
#agnetic poles o& brakes are energi(ed by a winding supplied with current &rom the
battery" Then the magnetic &lu) is distributed oer the rail" The eddy currents are
generated in the rail* producing an electromagnetic braking &orce" This types o&
braking need an additional sa&ety power supply when there are breakdowns in the
electrical power supply"
+ept" o& Electrical , Electronics #"E"S"C"E* -uttippuram.
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E'ECTR1CA''8 EJC1TE+ E++8 CRRET BRA-E
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2" 3ER#AET #A6ET E++8 CRRET BRA-E
Recently* permanent magnet eddy current brakes hae been deeloped &or
subways* trams and local trains" These brakes need a mechanical actuator to turn the
magnets n an on and o&& position" The main adantage o& this type o& brake is sa&ety"
i"e" it does not need electrical power supply to energi(e the magnet"
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BRA-16 3/5ER CA'C'AT1/S
Sophisticated calculation methods &or the determination o& braking &orces o&
eddy current brakes are important &or the design o& the brakes"
$or a simple eddy current brake employing a thin non@magnetic disc as
copper the drag or braking &orce on the disc
where
I #agnetic &ield strength in 5ebers"
A 3ole &orce area in cm2"
> >elocity in cmsec o& mean radius o& disc under the poles"
T disc thickness in cm"
speci&ic resistance o& disc material at its operating temperature in micro
ohmscm"
Tor!ue $ K R m
5here R mean pole radius in meter"
3ower 3 2 T90 watts"
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Seminar Report 2004 Eddy Current Brake
E++8 CRRET BRA-E RE;1RE#ETS
An eddy current brake is an energy conerter &unctions is to conert the
kinetic energy o& a ehicle into heat and dissipate it such a rate to maintain the
temperature o& unit with in reasonable limits under ma)imum and prolonged braking
conditions" The energy absorbed by the brake is trans&ormed into heat by the currents
induced in the motor* and this is heat manly dissipated in surrounding air through the
medium o& suitable designed &ins the rotating member"
1n mountains area* continues braking &orce is needed &or a long time say
about hal& an hourF* at this condition* eddy current braking is more suitable to &unction
without oer heating" The use o& these retarders is by no means limited to mountain
on country" They can be adantageously employed on public serice ehicles on city
routes without &re!uent stops" But in this braking system there with out be any
braking &orce in the ehicle is rest" So the eddy current brake is used as an au)iliary
heay@duty retarder" By using au)iliary retarder ery smooth retardation is assumed
and likely hood o& skidding on slippery roads sur&aces is minimi(ed" Smooth braking
action cuts down tier were and since brake is used as an au)iliary heay@duty retarder"
By using au)iliary retarder ery smooth retardation is assumed and likely hood o&
skidding on slippery roads sur&aces is minimi(ed" Smooth braking action cuts down
tier were and since the conentional brakes are relieed o& heay duty being re!uired
only to bring ehicles to rest"
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#/T16 A+ 1STA''AT1/
A typical mounting o& an eddy current brake consists o& two discs in which
pole salient type* supported between the &rame numbers o& a ehicle chassis" Rotor is
coupled to road wheels being o&ten mounted on a sha&t that is interposed between the
gearbo) and propeller sha&t and stator is mounted on the &rame o& the ehicle"
The drier who can select one or &our e)citation settings according to the
breaking e&&ect re!uired mounts a control switch on a steering column in a position
&or easy operation" 1n the operatie positions o& this switch .* 2* * 4 contractors are
energi(ed to supply current to the e)citation windings o& the retarder" 5arning lamp is
also proided on the instrument panel to indicate when the retarder is energi(ed" This
proides a sa&e guard &or the drier against leaing the unit energi(ed when the
ehicle is stationary"
+ept" o& Electrical , Electronics #"E"S"C"E* -uttippuram.
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A+>ATA6ES
'ess maintenance
5ide range o& braking &orce aailable within the temperature limit
3rolonged braking is possible
'ong li&e
'ess strain to the operation
Smooth retardation* which cuts down* the tire wears
Eddy current brakes o&&er smooth retardation o& ehicles without skidding" 1t
is totally &ree o& wear and tear" So it has long li&e compared to ordinary brakes" These
need less maintenance"
1n mountain areas continuous braking is needed &or a long time" At this
condition* eddy current braking is more suitable to &unction without oerheating"
By changing the e)citation current to the &ield winding* i"e" by adusting the
position o& the control switch* we can ary the braking &orce to re!uired range" The
operation o& eddy current brake is ery simple" i"e" the control switch is a so&t switch
which can be operated without any strain"
Eddy current brakes works een under the toughest enironmental conditions"
$or e)ample* in larger water slides and water coasters where the humidity would
immediately result in reduction o& &riction and thus impair the e&&ectieness o&
ordinary brakes" 1t works een in highly corrosie enironments and heaily
contaminated areas"
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+1SA+>ATA6ES
o breaking &orce at rest
eed o& electric power
The main disadantage o& the edyy current brake is that it needs electric power
to work" Researches are going on to oercome this disadantage by making the brake
regeneratie i"e" by conerting the kinetic energy o& the ehicle into electric energy
and storing it back into the battery"
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A33'1CAT1/S
$or additional sa&ety on long decants in mountain area
$or high speed passenger and goods ehicle
Eddy current brakes are best substitutes &or ordinary brakes* which are being
used nowadays in road ehicles een in trains* because o& their erk@&ree operation" 1n
mountain areas where continuous braking &orce is needed* &or a long time* the eddy
current braking is ery much use&ul &or working without oerheating" Eddy current
brakes are ery much use&ul &or high@speed passengers and good ehicles" 1t can also
be used to slow down the trolleys o& &aster roller coasters"
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C/C'S1/
Eddy current brakes are the best choice when demands &or reliability and
sa&ety are the highest" They work een in the toughest enironmental conditions" Een
the strike o& lightning will not result in the loss o& the braking &orce"
Eddy current braking system is not popular now a days" But we hope that the
eddy current braking system which is simpler and more e&&ectie will take the place o&
the ordinary braking system and we can do e)pect it to be the norm one in &ew years
o& time"
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RE$ERECES
." #anual . 6on(ale(* >olume 27*1ssue 4*Luly 2004
2" 1EEE Transactions on magnetics* >olume 4* 1ssue 4* Luly .==